Band gap modulation in polythiophene and polypyrrole-based systems

TL;DR

This study uses first-principles calculations to explore how substitutions and bilayer stacking in polythiophene and polypyrrole systems can modulate their electronic band gaps, providing insights for designing tunable organic electronic materials.

Contribution

It introduces a comprehensive analysis of band gap tuning in polythiophene and polypyrrole derivatives through substitutions and stacking, supported by both periodic and molecular calculations.

Findings

Substitutions lead to significant band gap changes.

Bilayer stacking results in linear band gap suppression.

Hybrid calculations confirm the trend in band gap modulation.

Abstract

In this paper, the structural and electronic properties of polythiophene and polyprrrole-based systems have been investigated using first-principles calculations both in periodic and oligomer forms. Of particular interest is the band gap modulation through substitutions and bilayer formation. Specifically, S has been substituted by Se and Te in polythiophene, leading to polyseleophene and polytellurophene, respectively, and N has been substituted by P and As in polypyrrole. The values obtained of the binding energy suggest that all the systems studied can be realized experimentally. Stacking (bilayer formation) of pure polythiophene, polypyrrole and their derivatives leads to linear suppression of the band gap or HOMO-LUMO gap as a function of the stacking. Mixed bilayers, including one formed from polythiophene on top of polypyrrole, have also been considered. Overall, a wide range of band gaps can be achieved through substitutions and stacking. Hybrid (B3LYP) calculations also suggest the same trend in the band gap as PBE calculations. Trends in the binding energy are similar for both periodic and molecular calculations. In addition, the $\Gamma$-point phonon calculation are performed in order to check the stability of selected systems.